Our preliminary cytochemical studies showed that the activities of some phosphatases mainly associated with the luminal plasma membranes of endothelial cells (EC) undergo changes in their polar distribution, which seem to be related to blood brain barrier (BBB) function. The goal of the present proposal is to expand these observations and to study relationships between the localization of certain enzymatic activities and BBB permeability. Our experiments will be performed on normal mice and on mice with damaged BBB by application of three different procedures: (a) mechanically induced lesion, (b) injection of hypertonic solution (mannitol), and (c) metabolic disturbance (insulin injection). Because in our pilot experiments we also observed increased BBB permeability and a redistribution of phosphatase activities in some small vessels in the brains of Scrapie-infected animals, mice innoculated with Scrapie agent will also be used. The localization of alkaline phosphatase (AP), 5'-nucleotidase (5'N), transport (Na ion K ion) ATPase and adenylate cyclase (AC) will be determined in cerebro micro-blood vessels employing ultrastructural cytochemistry. The permeability of BBB will be studied using the horseradish peroxidase (HRP) tracer. An attempt will also be made to study the distribution of Concanavalin A (Con A) receptors with concomitant localization of 5'N activity. Cytochemical incubation will be performed on either unfrozen, chopped sections, on ultrathin frozen sections of previously fixed brain or in situ through perfusion of the blood vessels with the incubation medium.